a) Field of the Invention
The present invention relates to a manufacturing method for an optical head device used to reproduce or the like from an optical recording disk such as a CD or a DVD and to an optical head device.
b) Description of the Related Art
In an optical head device, an emitted light beam from a light source is converged by an objective lens on the disk face of an optical recording medium (optical recording disk) and the reflected light beam is received on a light receiving element to perform reproduction of information or the like from an optical recording disk. Also, in the optical head device, a tracking error correction is performed by controlling the operation of the objective lens such that the beam spot of an emitted light beam follows a signal track on a disk surface with a high degree of accuracy.
As a signal detection system for the tracking error correction, a so-called three-beam system (one main beam and two sub-beams positioned on both sides of the main beam) is used to reproduce information from a disk of the CD system. In the three-beam system, a plurality of beams (sub-beam) are generated by a diffraction element and the detection of a tracking error signal is performed by the sub-beams.
On the other hand, for a disk only reading from a DVD system, the detection of a tracking error signal is performed by means of the one beam system in a broad sense which is referred to as the DPD (Differential Phase Detection) method. Also, the detection of a tracking signal is performed by means of the three beam system in a broad sense, which is referred to as the DPP (Differential Push Pull) method for a recordable type disk such as a DVD-R (DVD-Recordable) and DVD-RW (DVD-ReWritable).
In order to detect the tracking error signal by the three beam system, it is necessary to adjust the angular position (phase adjustment) of a diffraction element about the optical axis such that the line connecting the spot positions of the sub-beams on the optical recording disk forms a prescribed angle with the track tangential direction to adjust the spot positions of the sub-beams on the optical recording medium.
The two-wavelength optical head device in which reproducing and recording information is possible for a disk of both a DVD system and a CD system requires a first light source which emits a first laser light beam for reproducing and recording information on a disk of the DVD system and a second light source which emits a second laser light beam for reproducing and recording information on a disk of the CD system. Further, for the detection of a tracking signal by the three beam system for both disks of the DVD system and the CD system, a first diffraction element corresponding to the disk of the DVD system and a second diffraction element corresponding to the disk of the CD system are required as a diffraction element for the tracking error detection because the wavelengths of the laser beams, the track pitches of the disks and the like to be used for reproducing and recording are different.
Accordingly, in the final step of its manufacturing processes for the two-wavelength optical head device, the first laser light source and the second laser light source on a device frame are respectively turned on and a return light beam from an optical recording disk is received with a light receiving element and the angular positions of the first diffraction element and the second diffraction element about the optical axis are adjusted while monitoring the output signal. (see, for example, Japanese Patent Laid-Open No. 2000-251268, Japanese Patent Laid-Open No. 2001-52355, Japanese Patent Laid-Open No. 2000-285494, and Japanese Patent Laid-Open No. 2001-56955).
However, when the size of the optical head device is reduced, the space for mounting the diffraction element also becomes small. Therefore, in the final step of manufacturing processes for the two-wavelength optical head device, a considerable time and labor is imposed that the angular positions of the two diffraction elements about the optical axis are adjusted on the device frame while the respective light sources are turned on and the light receiving result of the return light beam from the optical recording disk is monitored.
Further, when the downsizing and assembling of the optical head device is improved by utilizing an optical module in which optical components such as a light source, a light receiving element and a diffraction element are modularized in a package, considerable time and substantial labor is imposed to respectively adjust the angular positions about the optical axis of the two diffraction elements, which are mounted in close proximity in a small space within the package, in the state that the optical module is mounted on the device frame while the respective light sources are turned on and the light receiving result of the return light beam from the optical recording disk is monitored.